Toll-Like Receptors (TLRs) are a primary mean whereby the innate immune system recognizes and rapidly responds to microbes. Studies employing the mouse models of toxoplasmosis indicate that the Myeloid Differentiation Factor 88 (MyD88), an adaptor-signaling molecule for the TLRs, is critical for initiation of early inflammatory responses and host resistance to infection with T. gondii. At least three TLRs (i.e. TLR2, TLR4 and TLR11) are involved in activation of the innate immune system and host resistance during T. gondii infection in mice. Human TLR 11 has a stop codon making this protein apparently nonfunctional. The main goal of our project is to characterize mechanisms whereby the human innate immune system responds to infection with T. gondii. Specifically, we will test the hypotheses that in humans, TLRs are key cognate receptors involved in the innate immune response to T. gondii tachyzoites, influence development of cell- mediated immunity, and that polymorphisms in TLRs related molecules affects human susceptibility to T. gondii infection. We will characterize the ability of tachyzoites, including their glycosylphospatidylinositol (GPI) and glycosylinositolphospholipids (GIPLs) or other glycolipids, as determined by a lipidomic approach, to bind and signal human cells via TLRs. Our focus will be on TLR2 and TLR4. Using single nucleotide polymorphisms (SNPs) we will look for allelic variation in the genes encoding the relevant TLRs as well as proteins in the signaling pathways that are critical for the functions triggered by TLRs. To determine whether there are associations with disease due to T. gondii in humans, we will characterize TLRs in patients with congenital toxoplasmosis and their parents, and in patients with ocular toxoplasmosis that remains stable or that recurs frequently. We will also evaluate whether allelic variations in TLR genes influence innate and acquired immunologic responses elicited by T. gondii in asymptomatic as well as patients with congenital disease, or acquired ocular toxoplasmosis. T. gondii causes eye disease and neurologic damage in congenitally infected individuals;in addition it affects immunocompromised persons and eye disease in a proportion of those who acquire T. gondii postnatally. Identification of the mechanisms of innate immunity involved in parasite recognition and that influence immune response during T. gondii infection will provide important information about new-strategies that may be applicable in vaccine development and therapy of human toxoplasmosis that maybe used to control parasite transmission, lessen the pathologies mentioned above and to improve the prognosis of the disease.